It’s "controversial" and, supposedly, "ethically questionable". The PARAMEDIC2 trial – designed to test whether or not adrenalin is useful in treating people who have a cardiac arrest out of hospital – is currently subject to a torrent of criticism.

Patients who are in cardiac arrest will be given either a dummy drug (the placebo), or the active drug, adrenalin. The paramedics or patients won’t know which the patient is given. The rest of the treatment will be just the same – cardiopulmonary resuscitation and electrical shocks to the heart as needed. The trial will be able to work out whether adrenalin saves lives or whether it is actually harmful.

The only ethical problem I have with this trial is that it hasn’t been done decades ago.

The concern alleged is that patients can’t give consent. Clearly, unconscious patients whose heart has stopped can’t have a study explained to them, take time to consider it, ask some questions, agree to take part and sign a consent form. That's the normal way of recruiting people for trials, and rightly so. But if we accepted this as the only ethical way to do a trial, it would mean that no studies would ever get done on unconscious people, which would be actively harmful. We would simply continue to give treatments that we "think" work as opposed to doing things that were proven to work.

This does damage to patients. When I was a junior doctor, it was thought, apparently quite reasonably, that steroids were good drugs to use where people had head injuries. They had been used for decades. Since brain damage often occurs due to the swelling of the brain and steroids are good at reducing swelling, it seemed absolutely logical to use steroids. But they were an article of faith, not science. When researchers searched for the evidence that steroids they were useful, they were disappointed. They could not be sure that these drugs, in routine use, were doing any good. They went on to do a trial – amid much criticism of "the ethics" of giving unconscious patients dummy drugs – and found that the steroids actively harmed people, with more deaths and disability recorded when they were used compared to placebo.

The difference between medicine and quackery is that medicine should be based on good-quality evidence – not opinion. We in medicine need to be much more honest about what we don’t know. It’s only "ethically questionable" to keep doing things that aren’t based in evidence.

Margaret McCartney is a GP in Glasgow who writes about evidence-based medicine